Advancing intravascular ultrasonic palpation toward clinical applications

This paper describes the first reported attempt to develop a real-time intravascular ultrasonic palpation system. We also report on our first experience in the catherization laboratory with this new elastographic imaging technique. The prototype system was based on commercially available intravascular ultrasound (US) scanner that was equipped with a 20-MHz array catheter. Digital beam-formed radiofrequency (RF) echo data (i.e., 12 bits, 100 Hz) was captured at full frame rate from the scanner and transferred to personal computer (PC) memory using a fast data-acquisition system. Composite palpograms were created by applying a one-dimensional (1-D) echo tracking technique in combination with global motion compensation and multiframe averaging to several pairs of RF echo frames that were obtained in the diastolic phase of the cardiac cycle. The quality of palpograms was assessed by conducting experiments on vessel phantoms and on patients. The results demonstrated that robust and consistent palpograms could be generated in almost real-time using the proposed system. Good correlation was observed between low strain values and regions of calcification as identified from the intravascular US (IVUS) sonograms. Although the clinical results are clearly preliminary, it was concluded that the prototype system performed sufficiently well to warrant further and more in-depth clinical investigation.